The present invention relates to a composite, flexible film of highly improved properties. More particularly, the present invention relates to a packaging film for forming self-sealed containers which may be easily transported in essentially flat, compressed form and which are capable of retaining 5 to 20 or more liters of liquid or semi-liquid content without succumbing to the physical stresses caused by movement or shift of the liquid within the containers.
Conventional containers for transporting and storing large volumes of liquid or semi-liquid content, e.g., ketchup, syrup, wine or the like, involve the use of containers of fixed dimensions, such as cans and cartons. These rigid containers have numerous drawbacks. Due to their rigid construction, the rigid containers must be unusually strong to withstand the physical stresses exerted by the liquid or other matter within the container. This is particularly true with larger volumes of liquid or semi-liquid materials which may shift during transport. Moreover, the use of a rigid container of heavy construction makes it uneconomical to transport such containers unless they are filled. Even when empty, the rigid containers occupy their full volume. Therefore, for commercial use, the rigid containers must be produced close to the site of filling and may not be reused, due to the high transport cost.
The flexible packaging film, and container produced therefrom, of the present invention permits the production of a lightweight, flexible container which may be employed to package substantial volumes and/or weights of liquid, semi-liquid and solid materials. The flexibility and strength of the film of the present invention, even for large containers, permits the container formed therefrom to contain volumes of, for example, from 5 to 20 liters, and weights of, for example, 20 to 30 kilograms. Moreover, since the film and the containers formed therefrom are flexible, such containers may be compressed into essentially flat form when they are empty to permit them to be easily and economically shipped, stored, transported and reused in both the filled and empty conditions.
Additionally, the flexibility of the films permits the container formed therefrom to withstand greater physical stresses caused by shifts in the container's contents than equivalently sized rigid containers. The physical stresses caused by the contents shifting may be absorbed by movement and stretching of the container wall. This enables the containers of the present invention to be composed of material of significantly lower strengths and weight than those employed in rigid containers of equivalent size. Such flexible film containers are disclosed in U.S. Pat. Nos. 4,085,244 and 4,096,309 to Stillman. The film disclosed in U.S. Pat. No. 4,085,244 comprises, in order from outside in, an outer layer of balanced biaxially oriented polyamide, a flexible metal foil, a layer of balanced biaxially-oriented polypropylene and an inner layer of heat-sealable, medium density polyethylene or polypropylene. However, difficulties have been experienced in the use of such films.